1. Technical Field
The invention relates to a method of recording an information signal representing at least one information unit on a record carrier having a recording track which comprises preformed track position information indicative of predefined locations for consecutively recording the information units and a first one of said locations comprising an earlier recorded information signal, said method comprising: generating from the information signal a modulated signal having successive frames, each frame including a synchronizing signal, and scanning said recording track and recording the modulated signal at a second one of said locations, while controlling such recording so as to maintain a fixed relationship between the track position information and the synchronizing signals.
2. Related Art
The invention further relates to a device for recording an information signal representing at least one information unit on a record carrier having a recording track which comprises preformed track position information indicative of predefined locations for consecutively recording the information units and a first one of said locations comprising an earlier recorded information signal, the device comprising modulation means for generating from the information signal a modulated signal having successive frames, each frame including a synchronizing signal, and recording means for scanning said recording track and recording the modulated signal at a second one of said locations, and for maintaining during said recording a fixed relationship between the track position information and the synchronizing signals.
A method and apparatus for successively recording information signals on a record carrier is known from U.S. Pat. No. 5,187,699. The information signal is modulated to a modulated signal having a frame structure comprising synchronizing signals for positioning the modulated signal in the track at predefined locations indicated by prerecorded track position information. The process of consecutively recording signals in adjacent areas in a track on the record carrier is called linking. In the known linking method, after a first recording signal is completely recorded, the recording process is continued after the last frame of the modulated signal up to a link position. When a next information signal is to be recorded, the recording process is started at the link position by recording dummy information (usually zero data) up to the start of the following predefined location. Hence the signal prior to the first frame synchronizing signal of said following location does not contain valid information. As a result a so called linking block is created between the first recorded signal and the second recorded signal, which linking block includes said link position. Hence the linking block does not contain valid recorded information, and its data storage capacity is lost.
It is an object of the invention to provide a recording method and device in which linking is more efficient.
For this purpose, the method as described in the opening paragraph is characterized in that in the event that the second one of said locations is after and adjacent to the first one of said locations, the recording is started before the end of a last frame of the earlier recorded information signal at a first predefined distance before a first synchronizing signal of the modulated signal. Further the device as described in the opening paragraph is characterized in that the recording means are arranged for determining if the second one of said locations is after and adjacent to the first one of said locations, and in such event starting the recording before the end of a last frame of the earlier recorded information signal at a first predefined distance before a first synchronizing signal of the modulated signal. By starting the recording within the last part of the earlier recorded signal, the signal in the next, adjacent area, i.e. said second location, is positioned at the nominal position and includes completely the first synchronizing signal as required by decoding circuits to decode the new data recorded at the second location. Hence the modulated signal at the second location is completely decodable. In fact the link position is located within the existing recorded information, and consequently the modulated signal at the first location is damaged in the very last part. Although this causes a few errors in the last symbols of the earlier recorded information unit, this proves to be preferable to losing an entire linking block. When the errors are unacceptable to the system, a system of error protection is applied to correct said errors. The measures according to the invention have the advantage, that no linking block is created and no storage capacity is lost, because the second location comprising the last recorded signal is directly adjacent to the first location comprising the previously existing signal. In addition any recorded data stream is not interrupted by invalid data from the linking block, which provides better compatibility with existing read-only record carriers, e.g. DVD-ROM or DVD-VIDEO.
The invention is also based on the following recognition. Usual channel coding and decoding systems are arranged to operate on symbols (e.g. 8 or 16 channel bits). When during decoding a read signal from the link position is decoded, the decoder will be confronted with a shift of the symbol boundary, a so called bit slip of a few bits, because it is in practice hardly possible to start the recording process with an accuracy of less than one bit. As a result the decoder will detect errors in all symbols for the full remaining part of the frame up to the next synchronizing signal. In prior art systems this posed no problem, as the linking block did not contain useful data. However the inventors have seen, that by selecting the linking point in the last part of the existing frame only a few errors would arise, which further may be correctable by modern error correcting codes.
A first embodiment of the device has the advantage, in the event that a new recording is to be made before and adjacent to an existing one, that the first synchronizing signal of the existing recording is not damaged, and only a predictable and low number of errors is generated when decoding the last recorded signal.
A second embodiment of the device has the advantage, that the physical starting point of recording is varied. This has the effect that disturbing read signal values are prevented, while the data is not shifted from its actual position.
A third embodiment of the device has the advantage that, by using variable random data instead of a fixed pattern in said interval, the sign of the synchronizing signal is also randomly varied for subsequent overwrite cycles of the same location. Hence material defects in the recording layer of said location due to repeated writing of the same patterns are counteracted.
Further advantageous embodiments according to the invention are given in the further dependent claims.